1. Field of the Invention
The present invention relates generally to gas-cleaning equipment and in particular to equipment for removing particulate matter entrained within a gas stream, wherein an electrostatically enhanced filter assembly for removing the particulate matter from the gas stream is employed.
2. Discussion of the Prior Art
A type of gas-cleaning equipment for removing particulate matter entrained within a gas stream that is in wide-spread use is the so-called electrostatic precipitator. An electrostatic precipitator typically includes high voltage discharge electrodes that ionize the gas stream as it passes by the electrodes and impart an electric charge to, i.e., ionize, the particulate matter entrained in the gas stream. Typically the charged or ionized particulate matter flows to electrically grounded stacks of large flat metal plates at which the particulate matter is removed from the gas stream and at least temporarily collected. The gas stream from which the particulate matter has been removed is then exhausted from the gas-cleaning equipment. Various types of mechanical means, such as “rappers”, for example, that intermittently strike the collector plates and dislodge the particulate matter collected at the plates, can be provided for removing the collected particulate matter. In many designs, the dislodged particulate matter slides or falls downwardly to hoppers where the particulate matter is accumulated for disposal.
A type of electrostatic precipitator that also is employed, and under many circumstances can more efficiently remove the particulate matter entrained in the gas stream, is an electrostatic precipitator that employs filter assemblies, rather than large flat metal plates, for removing and collecting the particulate matter. In this type of precipitator, each filter assembly typically includes a filter element and a supporting structure for the filter element. The filter assembly is electrically grounded, and the particulate matter which has been electrically charged, as by high voltage discharge electrodes, flows to the filter assembly where the particulate matter is removed from the gas stream and collected. Because this type of an electrostatic precipitator is designed so that the gas stream can only be exhausted from the precipitator after passing through the filter element, an enhanced degree of particulate matter removal can take place at the filter element because the gas stream with the entrained particulate matter must first pass through the filter element, where the particulate matter is removed and at least temporarily collected, before the gas stream is exhausted from the precipitator. Various means known to those having ordinary skill in the art can be utilized for dislodging the particulate matter that collects at the filter assemblies. Typically, the particulate matter, as it is dislodged, falls into bins or hoppers where the particulate matter accumulates until it is removed.
It can be the case with electrostatic precipitators that employ filter assemblies for removing and collecting the particulate matter from a gas stream that electrical fields are created at the filter assemblies by the high voltage discharge electrodes that are used to impart an electrical charge to the particulate matter. These electrical fields can be detrimental to the filter elements of the filter assemblies under the operating conditions to which the electrostatic precipitators are subjected. This is particularly the case where a fabric filter element is used. Oftentimes, the fabric filter element will develop holes through which the gas stream with entrained particulate matter can flow and be exhausted from the precipitator. Thus, the ability of the fabric filter to remove the particulate matter from the gas stream can be compromised in those instances.